Preliminary Study on Insecticidal Potential and Chemical Composition of Five Rutaceae Essential Oils against Thrips flavus (Thysanoptera: Thripidae).

To meet the demand for novel pest management strategies to combat the development of insecticide resistance, plant essential oils may be a promising alternative source. This study investigated the insecticidal activity of five essential oils from the Rutaceae plant family against Thrips flavus Schrank (Thysanoptera: Thripidae) under laboratory conditions. The plant essential oils were citrus oil (Citrus reticulata Blanco), Chuan-shan pepper oil (Zanthoxylum piasezkii Maxim.), zanthoxylum oil (Zanthoxylum bungeanum Maxim.), pomelo peel oil (Citrus maxima (Burm.) Merr.) and orange leaf oil (Citrus sinensis (L.) Osbeck). Among the essential oils evaluated, orange leaf oil (LC50 = 0.26 g/L), zanthoxylum oil (LC50 = 0.27 g/L), and pomelo peel oil (LC50 = 0.44 g/L) resulted in a higher gastric toxicity under laboratory conditions. The results of the pot experiment also showed that orange leaf oil (93.06 ± 3.67% at 540.00 g a.i.·hm-2, 97.22 ± 1.39% at 720 g a.i.·hm-2, 100.00% at 900.00 g a.i.·hm-2) zanthoxylum oil (98.73 ± 1.27% at 900 g a.i.·hm-2), and pomelo peel oil (100.00% at 900 g a.i.·hm-2) exhibited a higher control efficacy, being the most effective against T. flavus after 7 days of treatment. The essential oil components were then identified by gas chromatography-mass spectrometry (GC-MS). The insecticidal activity of orange leaf oil, pomelo peel oil, and zanthoxylum oil could be attributed to their main constituents, such as methyl jasmonate (50.92%), D-limonene (76.96%), and linalool (52.32%), respectively. In the olfactory test, adult T. flavus were attracted by zanthoxylum oil and Chuan-shan pepper oil. We speculated that linalool might be the key signaling compound that attracts T. flavus. These results showed that orange leaf oil, zanthoxylum oil, and pomelo peel oil exhibited insecticidal activities under controlled conditions. They can be implemented as effective and low-toxicity botanical insecticides and synergistic agents against T. flavus.

Parasitism and Suitability of Different Egg Ages of the Leguminivora glycinivorella (Lepidoptera: Tortricidae) for Three Indigenous Trichogramma Species.

Pod borers are economically important soybean pests in temperate and tropical regions. However, the biological control of these pests using their natural insect enemies has been poorly studied to date. Indigenous natural populations of three Trichogramma (Hymenoptera: Trichogrammatidae) species, Trichogramma chilonis Ishii, Trichogramma ostriniae Pang & Chen, and Trichogramma leucaniae Pang & Chen, were collected from Leguminivora glycinivorella (Matsumura) (Lepidoptera: Tortricidae) eggs in soybean fields in China. In this study, we compare the parasitic capacities and suitabilities of three indigenous Trichogramma species on L. glycinivorella eggs at various ages. Host eggs of all ages were accepted by T. chilonis, T. ostriniae, and T. leucaniae. T. chilonis tended to parasitize 0-2-d-old eggs more than 3-4-d-old eggs. There were no significant differences in parasitism between the 0-2-d-old eggs and the 1-4-d-old eggs for T. ostriniae and T. leucaniae. For eggs at various ages, T. chilonis parasitized the smallest number of eggs, while T. leucaniae and T. ostriniae exhibited similar parasitic capacities. With 0-d-old host eggs, T. ostriniae developed over the longest time period (8.7 d), and T. leucaniae produced the most female progeny (87.9%). Both T. leucaniae and T. ostriniae had similar developmental times, survival rates and percentages of female progeny with 1-3-d-old eggs. These results show that T. leucaniae can parasitize host eggs at varying ages with the best development and suggest that it may be a valuable biological control agent for soybean pod borers.

Development, Survival, and Reproduction of Megacopta cribraria (Heteroptera: Plataspidae) at Different Constant Temperatures.

The plataspid Megacopta cribraria (F.), an economic pest of soybeans, Glycine max (L.) Merrill, in Asia recently invaded North America and has become not only an important pest of soybean but also a nuisance pest. Although much is reported about M. cribraria in its native and invasive range, little information has been documented on the effect of temperatures on its development, longevity, and reproduction. We evaluated the influence of five constant temperatures (17-33°C) on the development, survival, fecundity, and population growth of M. cribraria in the laboratory. The developmental time for egg and nymph stages was shortened significantly with increasing temperature. The developmental time from egg to adult emergence was 114.81, 76.26, 44.54, and 38.54 d at 17, 21, 25, and 29°C, respectively. The nymphs of M. cribraria could not complete full development at a constant 33°C. The developmental threshold temperature estimated for egg to adult was 14.25°C, with a thermal constant of 849.56 degree-days. Females had the longest preoviposition period at 21°C (54.33 d), and the preoviposition period was shortened significantly as the temperature increased. Females had the longest oviposition period (35.33 d) and the highest fecundity (159.67 eggs per female) at 25°C and did not lay any eggs at 17°C. Female longevity was found to be shortest (44.0 d) at 29°C, and similar (75.67-81.50 d) at 17-25°C. The population trend index of M. cribraria was the highest (46.47) at 25°C, followed by 29°C (10.84) and 21°C (6.70). The results will be useful for predicting the phenology and population dynamics of M. cribraria and will provide some biological information on the invasive species in its nonnative range.

Performance of two egg parasitoids of brown marmorated stink bug before and after cold storage.

Introduction: The genus Trissolcus includes a number of egg parasitoids that are known to contribute to the control of Halyomorpha halys. The number of progenies, particularly females, is important for the efficient mass rearing of species used in augmentative biological control programs. Cold storage is an important technique for extending the shelf life of natural enemies used in such programs. Methods: We assessed how fecundity, sex ratio, lifespan, and the number of hosts parasitized within 24 h were affected by host density for T. japonicus and T. cultratus when offered fresh H. halys eggs and how these parameters were affected if adult parasitoids were first placed in cold storage (11°C in the dark) for 19 weeks before being used for propagation. Results: The fecundity were 110.2 and 84.2 offspring emerged at 25°C, for parasitoids not placed in cold storage; among the offspring that emerged, 82.6% and 85.6% were female for T. japonicus and T. cultratus, respectively. If first placed in cold storage, T. japonicus and T. cultratus produced 35.1 and 24.6 offspring per female, respectively, although cold storage significantly extended the shelf life. The survival rates of parasitoids that were placed in cold storage were 90.3% and 81.3% for females, and 3.2% and 0.9% for males of T. japonicus and T. cultratus, respectively. The number of hosts parasitized within 24 h was not shown to be density dependent, but it was significantly lower after cold storage. Discussion: This information can be used to estimate the likely production for augmented rearing colonies for use in biological control programs.

Effects of Temperature on the Development and Fecundity of Atractomorpha Sinensis (Orthoptera: Pyrgomorphidae).

Over the recent years, Atractomorpha sinensis I. Bolivar, has emerged as an important agricultural pest in China. However, the biological characteristics of A. sinensis remain largely unknown, which can hinder the prediction of its population dynamics. Thus, understanding the impact of temperature on the developmental period of A. sinensis is crucial to predict its population dynamics. The biological characteristics of A. sinensis were systematically observed at five different temperatures (16, 20, 24, 28, and 32°C) using the age-stage, two-sex life table method. The results demonstrated that the developmental period, preadult time, adult longevity, adult preoviposition period, and total preoviposition period were significantly reduced when the temperature was elevated from 16 to 32°C. The developmental threshold temperatures of egg, nymph, preoviposition period, female adult, male adult, and generation were 9.14, 10.44, 12.53, 10.97, 12.47, and 10.58°C, respectively, with the corresponding effective accumulated temperatures of 452.31, 575.99, 169.58, 528.13, 340.81, and 1447.95 degree-days. With an increase in temperature, the intrinsic rate of increase (r) and finite rate of increase (λ) were increased, while the mean generation time (T) was shortened. The optimal values of net reproductive rate (R0= 73.00 offspring) and fecundity (244.55 eggs) were determined at 24°C. Similarly, the population trend index (I) of A. sinensis was found to be highest at 24°C. Our findings indicate that A. sinensis has the greatest rate of population growth at 24°C, which can provide a scientific basis for predicting the in-field population dynamics of A. sinensis.

Comparative Transcriptome Analysis of Megacopta cribraria (Hemiptera: Plataspidae) in Response to High-Temperature Stress.

Kudzu bug, Megacopta cribraria (Fabricius), is mainly distributed in southern China and has been considered an invasive species in the southeastern United States. Megacopta cribraria is a soybean pest with high-temperature resistance, but the molecular mechanisms underlying its thermal adaptation are largely unknown. Here, we performed comparative transcriptome analysis to unravel the molecular response of M. cribraria toward high-temperature stress. Following RNA-seq, we identified 93,959 assembled unigenes, 14,073 of which were annotated in M. cribraria transcriptome libraries. In addition, 127 differentially expressed unigenes (DEGs) were detected, 88 of them were significantly upregulated, whereas the remaining 39 genes were significantly downregulated. Functional classification revealed that the pathways of metabolic process, cellular processes, and single-organism processes were considered to be significantly enriched. In the COG classification, DEGs were mainly localized into O: post-translational modification, protein turnover, chaperone. Moreover, protein processing in endoplasmic reticulum and linoleic acid metabolism were significantly enriched among the 38 KEGG pathways. Further gene annotation analysis indicated that nine heat shock protein-related genes were significantly upregulated. Finally, five HSP DEGs were selected for real-time quantitative polymerase chain reaction validation and demonstrated a similar upregulation trend with RNA-seq expression profiles. Taken altogether, these findings provide new insights into the molecular mechanisms of thermal adaptation in M. cribraria.

Toxicological characteristics of edible insects in China: A historical review.

Edible insects are ideal food sources, which contain important nutrients and health-promoting compounds. With a rapid development of industrial insect farming, insect-derived food is a novel and emerging food industry. Edible insects have been traditionally consumed in various communities, while continuously gaining relevance in today's society; however, they currently remain underutilized. Although there are a large number of literature on edible insects, these literature primarily focus on the nutritional value edible insects. The toxicity assessment data of edible insects remain incomprehensive, especially for the new national standard that is currently in effect; and many data and conclusions are not accurately specified/reported. Therefore, we performed a literature review and summarized the data on the toxicological assessment of edible insects in China. The review first describes the research progress on safety toxicological assessment, and then offers references regarding the development of 34 edible insect species in China. These data can be a platform for the development of future toxicological assessment strategies, which can be carried out by a multidisciplinary team, possibly consisting of food engineers, agronomists, farmers, and so on, to improve the acceptability of edible insects.

Effect of Temperature on the Development, Survival, and Fecundity of Heliothis viriplaca (Lepidoptera: Noctuidae).

Heliothis viriplaca (Hüfnagel) (Lepidoptera: Noctuidae) is worldwide an important economic pest of major agricultural crops. The effect of temperature on the biology, in particular the duration of the different developmental stages, of this insect pest was examined. The development, survival, and fecundity of H. viriplaca at five different temperatures (22, 25, 28, 31, and 34°C) were investigated, and experimental population life tables calculated. The results show that the developmental time of larvae, pupae, pre-oviposition, adults, and the entire generation decreases with increasing temperature. Larvae emerged fastest from the eggs at 28°C. The percentage of larvae that reached the seventh instar stage was 32.69, 38.60, 19.67, 3.61, and 20.88% at 22, 25, 28, 31, and 34°C, respectively. The developmental threshold temperature of the eggs, larvae, pupae, pre-oviposition and total pre-oviposition period was 10.53, 12.34, 5.60, 11.47, and 10.01°C, respectively. The effective accumulative temperature was 42.90, 239.68, 309.19, 77.72, and 767.64 degree-days, respectively. The population trend index (I) and the intrinsic rate of increase (r) of H. viriplaca were the highest at 31°C (133.97 and 0.12 d-1, respectively). The results of this study may be useful for predicting the population dynamics of H. viriplaca and thus provides information on this important insect pest that may assist in its management.